When manufacturing integrated circuits on a substrate for example silicon substrate, an implantation step of ionic species is required to locally dope the substrate and to allow carrying out N or P transistors. Prior to this implantation, the zones of the substrate which must not be implanted are protected by forming a mask generally formed of resin. After N- or P-type implantation for carrying out transistors, the top of the resin protecting the non-implanted zones is implanted at the same time. In order to finish the manufacture of the devices, it is then necessary to remove the mask. However, the traditional removal step of a resin by dry or wet method is not effective when the resin has been implanted beforehand. The implanted mask forms, indeed, a surface crust which is very difficult to be accurately removed and under conditions which do not damage the areas of the substrate not covered by the mask. It is then known to proceed to the removal of the mask in two steps. The first step consists in removing the surface crust, and then the second step consists in removing the underlying non-implanted resin. However, the first step requires the use of an aggressive etching chemistry which may damage and consume the silicon of the substrate in particular at the implanted source and drain, thereby degrading the performances of the devices.
A solution described by Kurt K. Christenson et al. in the publication ‘All Wet stripping Of Implanted Photoresist”, 8th International Symposium on Ultra Clean Processing of Semiconductor Surfaces UCPSS, 2006, uses a chemical solution called Piranha comprising a mixture of H2SO4 and H2O2. The drawbacks of this method lie in that said chemical solution shows a relatively slow reactivity with respect to the implanted resin and in that its reactivity towards the oxide SiO2 suggests a significant risk of damage of a silicon substrate.
An alternative to this method consists in performing a dry etching comprising a step of CF4/O2 plasma etching followed by a step of N2/O2 plasma etching generated by microwave at high temperature. Herein again, the damaging of the silicon substrate not covered by the mask during the first etching is such that it is not possible to accurately control the damaging of the N and P doped silicon zones.